1. Field of Invention
This invention relates to computer system peripheral devices and more specifically to synchronizing the real-time operations of computer system peripheral devices.
2. Description of Related Art
Most computer communication systems are designed for asynchronous data exchange. For example, a typical computer system includes an expansion bus adapted for coupling to one or more peripheral devices. Typical peripheral devices such as disk and CD-ROM drives generate and transmit multiple data units (i.e., blocks of data) in bursts followed by relatively long idle periods. Such peripheral devices arbitrate for control of the expansion bus in order to transfer data, and transmit the blocks of data according to a selected set of rules (i.e., protocol) during each expansion bus access period. Similarly, most network communication systems (e.g., local area networks) are also designed for asynchronous data communications. A typical network communication system includes multiple network devices (e.g., computer systems) connected to a common transmission medium (e.g., coaxial cable or twisted-pair cable). The network devices arbitrate for control of the transmission medium. Upon gaining control of the transmission medium, a given network device typically encapsulates packets into "frames" according to a selected network protocol and transmits the frames over the transmission medium. Each packet includes address and control information used to route the packet to its destination. Asynchronous data exchange allows bus and network communication systems to handle the "bursty" nature of data communications in an efficient manner.
A problem arises when two peripheral devices of a computer system exchange real-time audio or video information via, for example, the expansion bus. Reproduction of a live or recorded audio or video performance requires a substantially continuous flow of information. A data buffer is typically provided between a sending peripheral device and a receiving peripheral device in order to even out the flow of data. The sending device stores data within the data buffer, and the receiving device fetches the data from the data buffer as needed in order to reproduce the audio or video performance. Each peripheral device, however, typically includes a different clock generation circuit which determines the rate at which the device accesses the data buffer. Over time, if the sending device adds data to the data buffer faster than the receiving device fetches data from the data buffer, the data buffer will become full, data which cannot be stored within the data buffer will be lost, and the audio or video reproduction will be interrupted. Such a condition is known as data buffer overflow. Conversely, if the receiving device fetches data from the data buffer faster than the sending device adds data to the data buffer over time, the data buffer will eventually become empty and the audio or video reproduction will be interrupted. In this case, the result is a data buffer underflow condition. Unfortunately, no two clock generation circuits will operate at precisely the same frequency without external synchronization, and hardware synchronization methods require a direct connection between the two circuits for the exchange of timing information.
It would thus be desirable to have a system and method for synchronizing the data rates of devices exchanging real-time audio or video information. Such a system would not require a hardware connection between the two devices for synchronization, yet would substantially synchronize the operations of the devices in order to prevent data buffer overflow and underflow conditions.